According to JP-A-2004-144230, JP-A-2004-301294, and JP-A-2004-324882, electromagnetic valves (solenoid valves) are disclosed. A conventional structure of a solenoid valve is described in reference to FIGS. 11A, 11B. This solenoid valve is constructed of a spool valve 1 and a linear solenoid 2 for controlling hydraulic pressure through the spool valve 1. The linear solenoid 2 is constructed of a coil 13, a plunger 14 and a magnetic stator 15 for operating the spool valve 1. The magnetic stator 15 is a component of a magnetic circuit. The magnetic stator 15 is constructed of a yoke 17 formed of a magnetic material. The yoke 17 has a substantially cap shape, and covers the outer surface of the coil 13 and a stator core 21.
In this embodiment, the stator core 21 includes a magnetic attractive core 18, a slide core 20 and a magnetic interrupting portion 19, which are integrally coupled. The magnetic attractive core 18 generates magnetic force, thereby axially attracting the plunger 14. The slide core 20 is in a cylindrical shape covering the surface of the plunger 14, thereby being slidable relative to the plunger 14. The magnetic interrupting portion 19 interrupts magnetism between the magnetic attractive core 18 and the slide core 20. The plunger 14 is axially moved by changing conduction of an electric current to the coil 13, so that a spool 4 of the spool valve 1 is displaced in the axial direction thereof.
The stator core 21 has an unfixed axial end (free axial end), which is unfixed in the linear solenoid 2. Specifically, the stator core 21 is inserted through an opening of the yoke 17, and is fixed around the opening of the yoke 17 on the other fixed axial end of the stator core 21. Thus, one axial end of the slide core 20 on the axially opposite side of the fixed axial end of the stator core 21 is unfixed.
As shown in FIG. 11B, the unfixed axial end (free axial end) of the slide core 20 is a free end assembled into the inside of an insertion recess 22 formed in a cap bottom portion of the yoke 17. In this structure, the free end of the slide core 20 may abut the inner surface of the insertion recess 22 due to product dispersion of the stator core 21, an axial misalignment at an assembly work. In this case, this free end of the slide core 20 may be deformed, and the plunger 14 may not slide properly.
Accordingly, a sufficient assembly clearance (radial clearance) α radially between the free end of the slide core 20 and the insertion recess 22 is needed. As such, abutment between the slide core 20 and the insertion recess 22 is unlikely.
However, in this structure, a magnetic circuit is defined through this assembly clearance α. Therefore, magnetic transmission efficiency and magnetic attractive performance of the plunger 14 may be reduced, as the assembly clearance α increases. Specifically, the large assembly clearance α is needed between the free end of the stator core 21 and an adjacent magnetic circuit component in this linear solenoid 2, in which the free end of the stator core 21 is unfixed. Therefore, the magnetic attractive performance of the plunger 14 may become insufficient.